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In view of increasing concern over diesel particulates and tightening legislation to control their emission, much work has been done to develop diesel particulate filters (DPFs) and systems to allow them to work reliably. Although a filter will effectively trap solid particles, any material in the vapour phase, such as unburned hydrocarbons, may pass through the filter and subsequently condense. The use of a catalytic wash coat, either on the DPF itself or on a separate substrate, has been proposed to oxidise these hydrocarbons and thus reduce the total material emitted. The use of fuel borne catalysts to aid the regeneration of trapped material within the DPF is also well documented. Such catalyst will also catalyse the oxidation of any hydrocarbons bound up within the particulate. The oxidation of such hydrocarbon occurs at a lower temperature than that of carbon itself, thus allowing lower temperature regeneration of the DPF.

The atomisation characteristics of DI diesel engine fuel injection nozzles have been the subject of intensive study over the last decade. Much of this work has been related to clean, single hole nozzles spraying into quiescent air, at either ambient conditions or elevated pressures and temperatures. Experience shows that fuel injector nozzles may foul very rapidly in field service, and that this might have a significant effect on the performance of the engine particularly with regard to emissions. The build up of material on the injector nozzle can be controlled by the addition of suitable fuel additives. This paper describes test procedures developed to assess deposit build up and to indicate the efficacy of keep clean additives. The paper then goes on to describe high speed photographic techniques for studying the fuel spray characteristics of clean and fouled injectors in a firing engine.

Concerns over the effects of combustion chamber deposits (CCD) on engine performance coupled with increasing environmental pressures on vehicle exhaust emissions, have forced the original equipment manufacturers (OEMs) to call for control of fuel compositions to preclude or minimise deposit formation in the combustion chamber. However, this is currently not felt to be feasible, given the scarcity of data on the effect of CCD on emissions, and the lack of an industry standard measurement technique. This paper describes a two-year project which demonstrates the positive impact that a fully synthetic CCD control additive system has on engine performance and emissions. The same programme demonstrates that tailpipe HC, CO, and NOx all directionally increased after the deposit accumulation period, but only NOx decreased with the removal of CCD. Engine-out NOx emissions increase with heavy CCD weight.